When printing a PDF containing a graphic in png format the print quality of that text is badly reduced. I realized this issue when I got a new color printer (Brother DCP-9045CDN). Text is printed badly pixelized looking like 150dpi (without hinting). Printing the same text containing a jpg (or without) graphic instead of a png does not show this problem and text is printed just fine.
Printing the original document (incl png) directly from OpenOffice or printing the PDF with png from Windows with Acrobat Reader or OSX with preview works fine as well
Not a printer or driver issue
After some more investigation I realized that the problem also appears on other printers (tested with Brother HL-5250 and HP LaserJet 1210). Much less pronounced thought and therefore I haven't realized it before. Directly comparing the print out quality of PDF with png vs. one with jpg shows a slightly reduced text quality.
Screen rendering is fine in both cases, even when zooming in.
Is it not the application, its deeper in the stack
I used Okular to print the PDF but I also tested XPDF which shows the same behaviour. Using Acrobat Reader it prints "fine" but with a lower over all quality (looks like the document is turned into a picture before being sent to the printer).
Without being a specialist I assume that the problem is the PDF processing (poppler?) before its sent to the printer (Acrobat seems to use something different there).
I can provide example documents if required as well as print out examples.
BTW: this problem appears on Kubuntu 10.04 and 10.10